A network of the invention may include certain items that are common, as to their functions mentioned below, with a known network. These items include:
a plurality of terminals which are associated with as many respective user peripherals between which messages are to be transmitted;
two transmission lines associated with each of the terminals for transmitting waves, said transmission lines comprising an emission line for guiding emission waves emitted at an emission frequency of the terminal and a reception line for guiding waves received by the terminal; and
a star coupler for receiving waves which reach it via the emission line and for transmitting each of said waves to all of the terminals via the reception lines.
In such a network the emission frequencies of the various terminals vary over time. However, to avoid cross-talk, they must remain different and separated from one another by spectrum distances that are not less than a frequency increment. The frequency increment is selected to reserve a message channel of sufficient bandwidth within the spectrum range of the network. These frequencies thus constitute a sequence starting from a base frequency, which sequence is referred to below as a "stack" and it extends up to a stack top. This sequence corresponds to the sequence of message channels including said frequencies and also to the sequence of terminals that use said frequencies. In each of these sequences, an item may be adjacent to another item, i.e. it may precede it or follow it. The top of the stack is constituted by one of the emission frequencies, or for a call made over a plurality of frequencies by a group of such frequencies allocated to the same call, and mutually adjacent, for example, said frequency or said group being the furthest from the base frequency.
When a terminal is to transmit a message, it emits calling signalling including the address of a terminal that is to be called. If said terminal is ready to set up a call, it responds by emitting an acknowledge signal.
Said calling and acknowledge signalling and other signalling required to operate network is transmitted in the form of modulation on a carrier wave whose own frequency constitutes a signalling frequency. The frequencies of the modulated wave lie in a signalling channel which is reserved for said frequencies to one side of the message channels in the spectrum range of the network. The signalling channel is shared between all of the terminals that are not tuned to message channels in the sense that it may be used by all of said terminals.
A first known network is described in a first prior document constituted by European patent document EP-A-0 381 102 (F.degree. 16761). That document does not describe the existence of a signalling channel nor does it describe how to use one.
A second known network is described in a second prior document: "Protocols for very high-speed optical fiber local area networks using a passive star topology" (Isam M. I. Habbab, Mohsen Kavelhrad, and Carl-Erik W. Sundberg, Journal of Lightwave Technology, Vol. LT-5, No. 12, December 1987, pp. 1782-1793).
The spectrum range of said second known network includes a plurality of message channels and a signalling channel whose positions appear to be predetermined. The signalling channel is reserved for transmitting signalling of the kind mentioned above.
The spectrum range of a network of this type may be large if the mean number of messages to be transmitted per unit time said frequency increment and are themselves large. The increment is chosen to be large enough to enable messages having the highest data rate to be transmitted.
A particular object of the present invention is to improve in a simple manner the effectiveness with which the spectrum range of such a network is utilized.